Considerations of energy saving and reduction of pollution, particularly in an urban environment, are leading motor vehicle manufacturers to equip their models with an automatic system for stopping/re-starting the thermal engine, such as the system known by the term “stop and go”.
As recalled by the company VALEO EQUIPEMENTS ELECTRIQUES MOTEUR in patent application FR2875549, it is possible for vehicles to function according to the “stop and go” mode by means of a reversible electrical machine, or alternator-starter, which is coupled to the thermal engine, and is supplied by an inverter in “starter” mode.
The use of an alternator-starter system in a “stop and go” functioning mode consists in certain conditions of giving rise to complete stoppage of the thermal engine when the vehicle itself is at a standstill, then of re-starting the thermal engine, as the result for example of action by the driver which is interpreted as a request to re-start the thermal engine.
A typical “stop and go” situation is that of stoppage at a red light. When the vehicle stops at the light, the thermal engine is automatically stopped, then, when the light turns to green, the engine is re-started by means of the alternator-starter system, as the result of detection, by the system, of the clutch pedal being pressed down by the driver, or any other action which represents the wish of the driver to give rise to movement of his vehicle.
For this purpose, as the company VALEO EQUIPEMENTS ELECTRIQUES MOTEUR also indicates in patent application FR2875551, the “stop and go” system uses information representative of the state of functioning of the vehicle which is obtained from sensors of the vehicle, such as temperature sensors in the passenger space, or detection of the position of the clutch pedal, or information read on a data communication bus, such as the speed of the vehicle or the speed of rotation of the engine.
It will be appreciated that the automatic re-starting function carried out by an alternator-starter system is a function which must assure a certain level of safety of functioning.
As described by the company VALEO EQUIPEMENTS ELECTRIQUES MOTEUR in patent application FR287557, the essential characteristic of a method for controlling an alternator-starter system in starter mode is that it must comprise steps of verification of so-called prior conditions for re-starting of the engine before the re-starting phase takes place, and so-called “safety” conditions throughout the phase of re-starting of the engine.
A prior condition for restarting of the engine is determined in particular by at least one intentional action of the driver, for example pressing the clutch pedal down by more than 90%.
An additional condition is, for example, that the network on board the vehicle must be supplied, i.e. the contact key of the vehicle must be in the position +APC “after contact”, and the traction chain must be open.
In fact, when the vehicle is at a standstill (i.e. with zero speed) and the thermal engine is stopped by the automatic function, there is no question of re-starting the engine unless it is certain that the traction chain is open.
If the chain were closed, re-starting the engine could impel the vehicle, and consequently make it advance (or reverse), thus endangering the safety of property or people.
Thus, in order to avoid this type of situation, a solution is now implemented which uses a specific control line Auth. Ond., in order to authorise the control of the inverter. This specific control line Auth. Ond. is derived from a control system of the vehicle, which is external to the automatic stop/re-start function, thus fulfilling most of the safety requirements.
In addition, in order to detect the activated state of the electrical machine, a supplementary safety device is introduced. This safety device is constituted by the line Diag1. Ond., which conveys information which indicates the rotation of the electrical machine, and is obtained from signals from position sensors of the rotor.
This information is then put into form by the microprocessor for control of the electrical machine, and is transmitted to the microprocessor of the electronic control unit of the vehicle, amongst the state and faults signals.
This solution fulfils most of the safety requirements inherent in the function, but reveals certain disadvantages.
In fact, the information Diag1. Ond. is made available to the electronic control unit of the vehicle only when the microprocessor to control the electrical machine is functional. This involves a certain software delay in order to become reactive when the information is not present (delay to detect the absence of information).
Another disadvantage is that this solution requires use of a microprocessor with a large processing capacity, since the microprocessor to control the electrical machine must control and monitor the machine, as well as support all or part of the system strategy, whilst providing the interface towards the exterior.
This solution is also not suitable for the case in which the electrical machine is used both for re-starting of the thermal engine and for torque assistance.
A simple control line Auth. Ond. cannot be used to prevent both re-starting and torque assistance operations. In fact, the re-starting function can be activated only if the traction chain is open, whereas the torque assistance function can be activated only when the traction chain is closed. These two conditions are contradictory.
Nor does this known solution for making a stop/re-start solution failsafe derive benefit from the possible synergy between items of equipment on board, because of the presence of several microcontrollers within the system.
There is consequently a need for a new architecture which makes it possible to eliminate all of these problems, whilst increasing the level of safety of the global functionality.